1. Field of the Invention
The present invention relates to switching devices for circuits which interrupt the circuit upon the detection of leakage current, and more particularly to a switching device which interrupts the circuit upon the detection of leakage current in an appliance to prevent electrical shock.
2. Discussion of the Prior Art
Switching devices which interrupt a circuit upon the detection of leakage current or ground faults in the circuit for use with appliances are well known in the art. Appliances such as hair dryers, curling irons, electric shavers, and other personal grooming appliances are typically used in an environment where water is present which subjects the user to an increased risk of electrical shock. Many other appliances, such as heaters, radios, and the like, are also used in many cases in locations where water may be present, so that people occupying such areas are at risk to electric shock in the event a ground fault develops between the appliance and any surface water which may be present.
Consequently, a need has arisen to provide protection to users of such appliances to prevent inadvertent electric shock through carelessness or accidental placement of the appliance which subjects the appliance to a ground fault condition. In the appliance industry, it is now an important safety consideration to provide a circuit interrupting device which interrupts the electrical path from the power source to the appliance upon the detection of a predetermined leakage current level or ground fault condition in which the device instantaneously interrupts the circuit to prevent any further flow of electricity from the power source to the appliance.
In particular, safety testing organizations such as Underwriters Laboratories Inc. now require many appliances to have such a circuit interruption mechanism in order to pass the safety requirements designated for the particular appliance. In response to such requirements, many types of circuit interrupter devices have been developed in the prior art to provide means for instantaneously disconnecting the appliance from the power source upon the detection of a predetermined leakage current value or ground fault condition which would place the user at a potentially fatal risk of electric shock.
Typical circuit interrupter devices present in the prior art provide electromagnetic switching devices which utilize a solenoid having a movable core member which either retracts or extends to trip a mechanical linkage mechanism to instantaneously open the circuit to interrupt the flow of current to the appliance with which the circuit is used. Many of these devices provide means for resetting the circuit after the fault condition is eliminated, and the reset feature may be activated only upon removal of the dangerous condition.
Other types of circuit interrupters for use with electrical appliances provide a magnetic means in which a magnetic field is created to attract or repel a linkage member which will open the circuit upon the detection of a predetermined leakage current level. A typical device is shown in U.S. Pat. No. 4,706,153 to Sainomoto et al., which provides a magnetic core member which upon energization creates a magnetic field to attract a metallic member to the core to open the circuit upon the detection of leakage current. A transformer relay is provided which creates the magnetic field to attract the metallic member towards the core to open the circuit.
The devices shown in the prior art suffer several disadvantages which affect both the performance of the switching device and its cost of manufacture, which in many cases may prohibit a manufacturer of certain appliances from using such a device. For example, an important consideration in the hair dryer industry at this time is the cost of manufacture of the circuit interrupter switching device in relation to the overall cost of the hair dryer. It is not uncommon for many of the prior art devices to have a manufacturing cost which is at least 50% of the total cost of the hair dryer. Accordingly, many of the prior art devices utilizing elaborate mechanical linkages and interconnected members which trip the circuit in response to the energization of a solenoid resulting in the retraction or extension of a movable core member increase the cost of manufacture of the switching device to a prohibitive level for the appliance manufacturer. Furthermore, the incorporation of many moving parts and complex linkage mechanisms inside the switch requires greater spacing internally of the switching device and in many cases additional lubrication is necessary to insure instantaneous response of the device upon the detection of leakage current.
The novel appliance circuit interrupter switching device of the present invention obviates the disadvantages encountered in the prior art and provides an efficient and instantaneously responsive switching mechanism for interrupting an electrical circuit to an appliance upon the detection of a predetermined level of leakage current to prevent electrical shock to a user. The device of the present invention opens the circuit with a minimum of moving parts, which results in a low cost, yet highly reliable switching mechanism for lowering the cost of manufacture of the end use appliance.